Polyalkylene terephthalate resins such as polybutylene terephthalate resins (hereafter also referred to as “PBT resins”) exhibit excellent mechanical properties, electrical properties, and other physical and chemical properties, and also have good processability, and are consequently widely used as engineering plastics in a wide range of applications, including vehicle components and electrical and electronic components. Polyalkylene terephthalate resins can be used particularly favorably in applications such as casing materials for housing substrates with mounted electronic components, and insert molded articles containing an encapsulated sensor probe or connector terminal or the like, for the purpose of protecting the internal components from external moisture and dust, and from damage caused by impacts and the like.
The insert molding method is a molding method in which a member (hereafter also referred to as the “insert member”) formed with a metal or an inorganic solid is placed inside the mold in advance and is then encapsulated inside an injection-molded resin, and in order to produce a component that utilizes the rigidity and/or conductivity of the insert member and the moldability of the resin, the insert molding method is widely used as a method that enables simplification of the molding process. However, because the coefficient of expansion and contraction (the so-called linear expansion coefficient) caused by temperature variation is extremely different for the polyalkylene terephthalate resin and the insert member, molded articles in which the resin portion is thin-walled, molded articles having portions with large variations in the wall thickness, and molded articles having a sharp corner or the like often suffer from problems such as cracking immediately following molding or cracking due to temperature changes during use. Further, when the molten resin flows around the insert member inside the mold and converges, a joint portion known as a weld is formed, and cracking that starts from this weld is also common. Accordingly, insert molded articles are currently somewhat limited in terms of potential applications and shapes.
On the other hand, these molded articles also require further improvements in heat shock resistance to withstand use in environments having severe variations in temperature, such as the inside of vehicle engine bays or outdoor environments, and sufficient impact resistance to enable their use as casings. In response to these requirements, for example, JP 2007-169367 A discloses a polybutylene terephthalate resin composition in which a prescribed amount of a thermoplastic elastomer or a core-shell polymer is added to a polybutylene terephthalate resin as an impact resistance improver.
Further, JP 2009-155448 A and WO 2008/032636 each disclose a polybutylene terephthalate resin composition in which prescribed amounts of a core-shell polymer having a specific particle size and having a core layer constituted with an acrylic-based rubber, and glass fibers are added to a polybutylene terephthalate resin.